Effervescent formulations are a particularly acceptable way of presenting many drugs to patients, especially if they need to be taken on a long term or regular basis.
Effervescence is the evolution of bubbles from a liquid, for example as a result of chemical action. In the case of pharmaceutical products this gas is normally carbon dioxide which is liberated by the reaction between a physiologically acceptable acid (e.g. citric, tartaric or malic acid) and a source of carbonate (such as sodium carbonate, sodium bicarbonate or a mixture thereof). It is convenient for these basic and acidic components of the "effervescent couple" to be separately granulated (e.g. by wet granulation, preferably in water), dried and then combined prior to or during packaging. The resultant mixture will then produce effervescence on being added to water.
Morphine is a drug which is often taken on a long term or regular basis and although it is available in a number of forms it has so far not been produced in an effervescent formulation.
It is known that morphine is normally degraded by oxidation, promoted by a wide variety of circumstances, and that this occurs more readily in basic media. It would therefore appear obvious to incorporate the morphine into the acid component of the effervescent couple. A further advantage would appear to be that ascorbic acid could be incorporated in this acidic mixture as an antioxidant. When such a composition is made up however, it is found that a significant decrease in activity occurs during storage. Analysis shows that this is due to esterification of phenolic groups in the morphine by the acids.